The present invention relates to inductors, and in particular to forming inductors in leadframes for semiconductor packages.
Industry trends in wireless communications are forcing increased integration, size reduction, and cost reduction. Many radio frequency circuits require matching, filtering, and biasing networks, which require inductors having relatively high inductance values with low loss. In general, the higher the inductance value, the larger and more expensive the inductor. Further, the precision of the inductance for the inductor is proportional to its cost. In many applications, inductors contribute a significant portion of the overall cost of circuit implementation.
Traditionally, there have been four options available for providing inductance in association with an integrated circuit. The first and most common option is for the end manufacturer to add discrete inductors in their final assemblies in association with other integrated circuits and discrete components. Adding discrete inductors is an unattractive option for the end manufacturer due to the physical space required on the final assembly for the inductor and the cost of the inductor.
A second option is to implement the inductor using wirebonds. Wirebonds are thin wires or ribbons that typically connect portions of a semiconductor die to the leads in the semiconductor package. When implementing an inductor, the wirebonds may be used in traditional fashion between a bond pad on the semiconductor die and a lead, as well as between bond pads on the semiconductor die. Unfortunately, wirebonds provide limited inductance and have proven to be electrically lossy. A third option is to actually create or place an inductor on the semiconductor die. Implementing an inductor on a semiconductor die has proven to be very expensive, electrically lossy, and given the limited size of the die, unfeasible in providing higher inductance values.
A fourth option is to design a module package having a substrate on which an inductor may be incorporated through surface mount or printed circuit board fabrication techniques. This option has the same limitations as having the end manufacturer incorporate the inductor in its final assembly. The result is essentially passing the cost on to the module fabricator instead of the final assembler.
Accordingly, there is a need for a cost-effective technique for implementing and integrating inductors into semiconductor packages. There is a further need for these inductors to have sufficient inductance for matching, filtering, and biasing networks in wireless communication applications.
The present invention integrates an inductor into a semiconductor package by integrally forming inductive segments in the leadframe. The inductive segments may be connected directly to a lead of the leadframe, or indirectly to a lead or a bond pad on a semiconductor die via wirebonds to form an inductor. The inductance value for the resultant inductor is typically controlled by the point of contact for the wirebonds or the leads about the inductive segment. The inductance values may also be controlled by the shape and size of the inductive segments. The leadframe may be formed to support multiple inductive segments, and one or more configurations, including those using one or more die flags to support a like number of semiconductor die.